Hippocampus-sparing radiotherapy using volumetric modulated arc therapy (VMAT) to the primary brain tumor: the result of dosimetric study and neurocognitive function assessment.

BACKGROUND: We hypothesized that hippocampal-sparing radiotherapy via volumetric modulated arc therapy (VMAT) could preserve the neurocognitive function (NCF) of patients with primary brain tumors treated with radiotherapy. METHODS: We reviewed data from patients with primary brain tumors who underwent hippocampal-sparing brain radiotherapy via VMAT between February 2014 and December 2015. The optimization criteria for the contralateral hippocampus was a maximum dose (Dmax) of less than 17 Gy. For NCF evaluations, the Seoul Verbal Learning Test for total recall, delayed recall, and recognition (SVLT-TR, DR, and Recognition) was performed at baseline and at seven months after radiotherapy. RESULTS: A total of 26 patients underwent NCF testing seven months after radiotherapy. Their median age was 49.5 years (range 26-77 years), and 14 (53.8%) had grade III/IV tumors. The median Dmax to the contralateral hippocampus was 16.4 Gy (range 3.5-63.4). The median mean dose to the contralateral hippocampus, expressed as equivalent to a 2-Gy dose (EQD2/2), was 7.4 Gy2 (0.7-13.1). The mean relative changes in SVLT-TR, SVLT-DR, and SVLT-Recognition at seven months compared to the baseline were - 7.7% (95% confidence interval [CI], - 19.6% to 4.2%), - 9.2% (95% CI, - 25.4% to 7.0%), and - 3.4% (- 12.7% to 5.8%), respectively. Two patients (7.7%) showed deteriorated NCF in the SVLT-TR and SVLT-DR, and three (11.5%) in the SVLT-Recognition. The mean dose of the left hippocampus and bilateral hippocampi were significantly higher in patients showing deterioration of the SVLT-TR and SVLT-Recognition than in those without deterioration. CONCLUSIONS: The contralateral hippocampus could be effectively spared in patients with primary brain tumor via VMAT to preserve the verbal memory function. Further investigation is needed to identify those patients who will most benefit from hippocampal-sparing radiotherapy of the primary brain tumor.

Inclined head position improves dose distribution during hippocampal-sparing whole brain radiotherapy using VMAT.

PURPOSE: Hippocampal-sparing whole brain radiotherapy (HS-WBRT) aims to preserve neurocognitive functions in patients undergoing brain radiotherapy (RT). Volumetric modulated arc therapy (VMAT) involves intensity-modulated RT using a coplanar arc. An inclined head position might improve dose distribution during HS-WBRT using VMAT. MATERIALS AND METHODS: This study analyzed 8 patients receiving brain RT with inclined head positioning. A comparable set of CT images simulating a non-inclined head position was obtained by rotating the original CT set. HS-WBRT plans of coplanar VMAT for each CT set were generated with a prescribed dose of 30 Gy in 10 fractions. Maximum dose to the hippocampi was limited to 16 Gy; to the optic nerve, optic chiasm, and eyeballs this was confined to less than 37.5 Gy; for the lenses to 8 Gy. Dosimetric parameters of the two different plans of 8 patients were compared with paired t-test. RESULTS: Mean inclined head angle was 11.09 ± 0.73°. The homogeneity (HI) and conformity (CI) indexes demonstrated improved results, with an average 8.4 ± 10.0 % (p = 0.041) and 5.3 ± 3.9 % (p = 0.005) reduction, respectively, in the inclined vs. non-inclined position. The inclined head position had lower hippocampi Dmin (10.45 ± 0.36 Gy), Dmax (13.70 ± 0.25 Gy), and Dmean (12.01 ± 0.38 Gy) values vs. the non-inclined head position (Dmin = 12.07 ± 1.07 Gy; Dmax = 15.70 ± 1.25 Gy; Dmean = 13.91 ± 1.01 Gy), with 12.8 ± 8.9 % (p = 0.007), 12.2 ± 6.8 % (p = 0.003), and 13.2 ± 7.2 % (p = 0.002) reductions, respectively. Mean Dmax for the lenses was 6.34 ± 0.72 Gy and 7.60 ± 0.46 Gy, respectively, with a 16.3 ± 10.8 % reduction in the inclined position (p = 0.004). Dmax for the optic nerve and Dmean for the eyeballs also decreased by 7.0 ± 5.9 % (p = 0.015) and 8.4 ± 7.2 % (p = 0.015), respectively. CONCLUSION: Inclining the head position to approximately 11° during HS-WBRT using VMAT improved dose distribution in the planning target volume and allowed lower doses to the hippocampi and optic apparatus.

Dosimetric effects of the acuros XB and anisotropic analytical algorithm on volumetric modulated arc therapy planning for prostate cancer using an endorectal balloon.

BACKGROUND: To compare the dosimetric effects of Acuros XB (AXB) and Anisotropic Analytical Algorithm (AAA) on volumetric modulated arc therapy (VMAT) planning for postoperative prostate cancer patients irradiated using an endorectal balloon (ERB). METHODS: We measured central axis doses with film in a phantom containing an air cavity, and compared measurements with calculations of the AAA and AXB. For clinical study, 10 patients who had undergone whole pelvic radiotherapy (WPRT) followed by prostatic bed-only radiotherapy (PBRT) using VMAT were enrolled. An ERB was used for PBRT but not for WPRT. To compare dosimetric parameters, the cumulative dose-volume histograms, mean, maximum, and minimum doses were measured for the planning target volume. Homogeneity of plans were confirmed using V95%, V107% (VX%, percentage volumes receiving at least X% of prescribed doses) and conformity indices (homogeneity index [HI], conformity index [CI], and conformation number [CN]). We compared volumes of the organ-at-risk receiving 10% to 100% (10-tier at 10% interval) of prescribed doses (V10% - V100%). RESULTS: In the phantom study, the AAA showed larger disagreement with the measurements, and overestimated the dose in the air cavity, comparing with the AXB. For WPRT planning, the AAA predicted a lower maximum dose and V107% than the AXB. For PBRT planning, the AAA estimated a higher minimum dose, lower maximum dose, and smaller V107%, and larger V95% than the AXB. Regarding the conformity indices, the AAA was estimated to be more homogenous than the AXB for PBRT planning (HI, 0.088 vs. 0.120, p = 0.005; CI, 1.052 vs. 1.038, p = 0.022; and CN, 0.920 vs. 0.900, p = 0.007) but not for WPRT planning. Among V10% to V100% of the rectum, the PBRT exhibited significant discrepancies in V30%, V40%, V70%, V80%, and V90%; while the WPRT did in V20% and V30%. CONCLUSIONS: The phantom study demonstrated that the AXB calculates more accurately in the air cavity than the AAA. In the clinical setting, the AXB exhibited different dosimetric distributions in the VMAT plans for PBRT containing an ERB. The AXB should be considered for prostate cancer patients irradiated with an ERB for better applying of heterogeneous condition.